Eigenschaftsstreuungen bei Holzfaser-Hartplatten

Summary

The investigations led to the following conclusions:

• 1. Reducing the variation of the board thickness might be considered as one of the most important means for the improvement of the mechanical quality of hardboards. Since the variation in thickness seems to be caused mainly by irregularities during hot pressing, special attention must be given to this process. Excellent condition, careful treatment and, it necessary, renewal of the press cauls in time are as important as the irreproachable condition of the press plates and the prevention of slacknesses in the hotpress.

• 2. Extremely defective spots in hardboard might be due to incorrect gluing. It is probably the adhesive’s fixing process that accounts for this effect.

• 3. On the average most of the boards exceeded by far the quality specifications according to DIN 68750. On the other hand all minima values of the bending strength observed were far below the required value, especially those of 4 mm boards. The large variation proved, necessarily raises the question whether the specifications of DIN 52 352 ought to be altered or completed. These investigations show that from an average of 10 specimens no representative result, with regard to bending strength and specific gravity of tested boards, can be obtained. Under this aspect, a new redaction of DIN 52 352 should adapt the choice and the number of specimens to the variation of property of hardboards proved by these tests.